The invention relates to a biosensor system for detecting organic trace compounds particularly organic components in air resulting from smoldering fires or from plant damage utilizing a chemoreceptor.
Methods for the early detection of fires generally utilize optical sensors which measure the light scattering of aerosols. However, these methods have only limited reliability. Ionization detectors to measure the ionization current of ionized aerosols, which employ a radioactive preparation, are used less and less now.
The main reason herefor is the costly handling of the radioactive preparations. Thermocameras with which a temperature rise of 0.1.degree. C. can be detected over a large area, are also used for example for the surveillance of stored waste materials in waste combustion plants. However, such camera systems are expensive while their reliability is questionable. Recently, gas sensors on the basis of semi-conductors or electrochemical cells are increasingly used. They are used to measure the concentration of CO, of H.sub.2 with catalytically active surfaces, or of hydrocarbons. The detection sensitivity is about 1 ppm, the sensing reliability however may be detrimentally affected to various degrees by background gases such as motor vehicle exhaust gases (D. Kohl et al.: Gassorentechnik zur Erkenning von Schwelbraanden (gas sensor technique for the detection of smoldering fires) in "Brandmeldeanlagen", Vol 5 convention 1993).
It is a disadvantage of the known detection methods particular in the field of early fire detection that there is an insufficient selectivity and sensitivity for the substances which are sensed to provide adequate warming. In order to increase the detection reliability sensors are needed which permit the fire-specific detection of trace compounds with increased sensitivity.
It is furthermore problematic in integrated plant protection systems to determine the optimal point in time when to apply insecticides such that the least possible amount of insecticides is required and the chances for the destructive insects to become resistant to the insecticide are reduced.
Because of the great economical and ecological importance of this problem for the production of plants, various methods have been developed which are designed to determine the best point in time for treatment (R. L. Metcalf et al., Introduction of insect pest management, John Worley, & Sons, New York 1975).
These methods require either to walk the fields regularly and determine the population density by counting out the insects, or they utilize complicated computer simulation models of the insect population development which, however, can be utilized only locally and only in connection with particular types. A more universal method for determining the most suitable point in time for the application of insecticides resides in measuring the extent of the scent emissions generated by the plants as a result of their injuries. These emissions can be measured by conventional trace analysis methods such as gas chromatography in combination with mass spectroscopy (GC-MS) as well as by electroantennograms (EAG).
With the GC-MS method frequently used for trace analysis (J. Arey et al., Terpenes emitted from agricultural species found in California's Central Valley, J. Geoph. Res. 96 (1991) 9239-36), a high reliability and sensitivity is achieved on one hand, but on the other hand, the personnel and equipment costs as well as the time and space requirements are high as the equipment is voluminous and heavy. In contrast, the EAG method provides for a fast and highly sensitive detection of emissions in the range below 1 ppm as reported already by S. Schtitz et al. in Biosenser for plant damage by insects, Med. Fa. Lanbouww. University Gent, Belgium, 59/25(1994).
In this method, an insect is firmly held in place and the voltage drop at the insect antenna is measured by attaching a microelectrode to the free end of the insect antenna and another microelectrode to the end of the antenna adjacent the insect head. The electrodes are connected, by connecting wires, to a special signal processing unit which measures the depolarization voltage of the insect antenna in a time dependent manner while air containing trace components flows past the antenna.
This arrangement however, is electrically and mechanically unreliable and the life of the biosensitive component is only relatively short because of inappropriate adaptation of the insect antenna to the signal sensing electrodes. As a result, the arrangement has little flexibility in its operation and handling. In addition, the arrangement requires the use of micromanipulators for the stable coupling of the electrodes to the antenna. Also, the microelectrodes are very sensitive as they consist for example of glass and have a diameter of only, for example, 1 .mu.m.
It is the object of the present invention to provide a biosensor and a suitable method of making a biosensor which has a high sensitivity and selectivity and which is highly reliable and which is furthermore portable for use in the field as a detector for example for plant emissions and for fire-specific emissions such as multi-functional phenols alkenes or terpenes.